As a photoelectric conversion element by a semiconductor, light-emitting elements such as a light-emitting diode and a semiconductor laser as well as light-receiving elements such as a solar cell have been known.
The matter required for practical use and high performance of a light-emitting element is a high-power optical output and an increased longevity of an element. On the other hand, in a case of a receiving element, improvement of conversion efficiency is required. However, it is well known that a crystal fault (dislocation) that is inherent in a semiconductor crystal constituting a photoelectric conversion element inhibits the above high performance and deteriorates operation property.
With reference to FIG. 8, the condition that a crystal fault in a semiconductor crystal deteriorates operation property of a photoelectric conversion element will be explained.
FIG. 8 is a block diagram showing the configuration of a photoelectric conversion element 100 as one example. The photoelectric conversion element 100 includes an n-type semiconductor layer 101, an active layer (photoelectric conversion unit) 102 formed on the n-type semiconductor layer 101 and a p-type semiconductor layer 103 formed on the active layer 103. These are formed as a basic structure of a photoelectric conversion device by a well known semiconductor manufacture technique etc.
Here, a basic operation of the photoelectric conversion element 100 will be briefly explained with an example of a light-emitting element.
When a current is injected in the photoelectric conversion element 100, an electron is injected from the n-type semiconductor layer 101 and a hole is injected from the p-type semiconductor layer 103. The injected electron and hole are converted to a light by a luminescence recombination process in the active layer 102 and output a light to the outside.
However, the photoelectric conversion element may include a crystal fault (threading dislocation) 201 as shown in FIG. 8 due to configuration imperfection of a semiconductor crystal. FIG. 8 schematically shows a crystal fault which is inherent in a semiconductor crystal constituting the photoelectric conversion element 100 and there exist a threading dislocation 201 and a nonluminescence center 202. For example, the threading dislocation 201 that generates at an interface between a growth substrate and a growth layer and propagates from below to the photoelectric conversion element 100 behaves as the nonluminescence center 202 that inhibits photoelectric conversion in the active layer 102.
In particular, in a nitride semiconductor, the threading dislocation is commonly included with a high density of 1×108cm−2 to 1×1010cm−2, which becomes a major obstacle of high performance of a light-emitting element.
As a technology to reduce influence of this crystal fault, for example, Patent Literatures 1 and 2 below can be listed.